The present invention relates to garbage incinerators with a combustion chamber and a flue for the flue gas communicating therewith.
The incineration of garbage is connected with considerable difficulties, since the garbage may be of very different composition.
Since a complete combustion is desired, it is among other things necessary to take care of a suitable introduction and distribution of a sufficiently large amount of combustion air, which as a primary, secondary and tertiary air is introduced into the combustion chamber.
Domestic garbage and similar garbage has a very high percentage (about 80%) of volatile components (fumes), which must be subjected to an afterburning under addition of secondary air.
Thereby it is necessary to assure an intensive mixing of the fumes or flue gases with the secondary air, since otherwise only an incomplete combustion would occur.
Such a construction should assure that the flue gases revolve on the inclined surfaces of the incinerator and that thereby the mixing of flue gas and combustion air is favored.
During operation of such installations, it has however proved disadvantage that thereby flue gas detachment whirls are produced and the particles contained therein, which are in pasty condition, will settle at the rear wall inclination of the incinerator to cause considerable baking on the same.
During the incineration of garbage in incinerators efforts have been made to provide for the most possible complete combustion; in order to achieve this, on the one hand the greatest possible amounts of heat should be generated, and on the other hand, the amounts of unburned residues and noxious materials contained therein should be reduced. Inasmuch as garbage contains a considerable portion of volatile ingredients with the heat value up to 80% as compared to other solid fuels, only a partial combustion takes place immediately on the grate of the combustion chamber. Volatile ingredients are first vaporized. These ingredients are burned out in the transition zone between the combustion chamber and the flue. Only a portion of combustion air, or so-called primary air is correspondingly led through the grate of the combustion chamber. Usual combustion air is blown into the incinerator above the grate as secondary air. It is important that flue gases be supplied with the sufficient amount of combustion air uniformly over an entire cross-section of the incinerator.
To obtain such a mixing of fumes and secondary air the combustion chambers in garbage incinerators are usually so constructed that above the degasification zone the upwardly extending flue is restricted at its front and rear wall by non-symmetrically arranged projections and provided with secondary air nozzles arranged beneath these projections. Such an arrangement has been disclosed in German Pat. No. 1,289,938. It has been obtained by this rather costly means that a vortex or turbulence be produced in the stream of flue gas, which turbulence must cause an intensive intermixing of flue gas with secondary air. Nozzles for blowing secondary air for the combustion of volatile combustible ingredients have been usually arranged in the known device on the bottom walls forming the projections, respectively.
In practice, however, serious disadvantages have been found in the above described incinerators. The loosening vortexes formed by secondary air discharged from the nozzles arranged on the inclined noses or projections are loaded with particles highly concentrated in the air. Since an incomplete intermixing of flue gas with secondary air takes place in the transition zone these particles, due to local shortage of oxygen still contain unburned combustible ingredients. Those particles in the above described combustion process of the combustible volatile ingredients have a temperature at which they are in pasty, viscous state. When these particles come into contact with the wall surfaces of the incinerator they form on the upper sides of the projections cakes which, upon cooling of the incinerator, solidify. These cakes in unfavorable instances reach the weight of tons within the period of few months. These cakes must be removed from the surfaces of the incinerator by means of pneumatic hammers, which usually takes a few days or even weeks to do. Furthermore, chippings dropped from those cakes can lead to damaging of the combustion grate.
Owing to the non-symmetrical arrangement of the inwardly extended projections the speed, with which flue gas stream flows within the incinerator, has a speed component directed toward the wall of the flue. Ash entrained in flue gas stream causes at the places of impacts a strong erosive action on the surfaces of the incinerator. Moreover, the walls exposed to such an action in the conventional installations must be renewed in a short period of time.
It has been found practically impossible to distribute secondary air, which is blown into the incinerator through the nozzles arranged on the undersides of the projections, uniformly over the entire cross-section of the transition zone. In the case of the size of the combustion chamber being from 5 to 6 m, an impulse of air streams discharged from the nozzles is not sufficiently large to reach some remote places in the incinerator. Furthermore, it was not possible, for constructive reasons, to arrange the nozzles sufficiently tight or close to each other so that air streams blown from the nozzles could produce an uninterrupted air mist. It has been further discovered that even with a strong overstoichiometrical air supply, locks of carbon monoxide and other non-completely burned-out gases are still formed. These reduced locks of carbon monoxide can, upon contact thereof with the tubular wall of the flue, result in a tube burst. Moreover, the heat output is worsened and the emission of noxious materials into the atmosphere is increased. Air, which does not take part in combustion, loads the heat output because it increases the amount of the heated exhaust air. An insufficient admixture of secondary air with flue gas results in the formation of highly concentrated noxious gases, such as hydrochloric acid and sulfur dioxide, which cause strong local corrosion of the walls of the flue.